The present invention relates to a circuit print board manufacturing method and a circuit print board, in particular, to a circuit print board manufacturing method, a circuit print board, and a carbon sheet, in which a rise of a temperature of the board caused by down-sizing and integration of the circuit print board can be prevented.
According to recent down-sizing and integration of the electric device such as a portable computer and a cellular phone, a circuit print board installed in the electric device has been also down-sized and integrated from a single-sided board to a double-sided board and a multilayered board. However, as the down-sizing and integration of the circuit print board are performed, the rise of the temperature of the heating element itself, the temperature of the circuit print board, the temperature of the frame of the electric device due to the heat radiated from the heating element such as an LSI and a power amplifier installed in the circuit print board have become problems.
Under this circumstance, conventionally, as shown in FIG. 15, the heat is effectively released by thickening a copper plane layer 102 of a board 101. In another way, as shown in FIG. 15, a metal layer (Al heat spreader 103) having a good thermal conductivity such as aluminum is provided between the heating element such as an LSI 100 and a frame 104 so as to diffuse the heat generated by the heating element and to prevent the rise of the temperature.
When the heat is diffused and the rise of the temperature of the heating element etc. is prevented in the way as described above, however, there are some problems as described below: namely, the weight of the electric device increases because the density of the copper or the aluminum (mass per volume) is high; and further, it is required to have a space for installing the heat spreader, which may prevent the down-sizing of the electric device.
Graphite is known to have a smaller density than copper or aluminum and a good thermal conductivity in a plane direction. The Japanese Utility Model Gazette HEI 5-11475 disclosed a method for improving the heat radiation effect by inserting the graphite sheet into the board. However, this method relates to printing a circuit on one surface of the board, and is not applied to the board having a through hole. A double-sided board having the circuits on both sides or a multilayered board having the circuits formed on multiple layers has a through hole plated by the conductive material on the side surface. Since the graphite sheet has an electric conductivity, when the graphite sheet is simply inserted into the multilayered board, the graphite sheet makes short-circuit with the through hole.
As shown in FIG. 16, another prior art, Japanese Unexamined Patent Publication No. HEI 8-23183 disclosed a partial cross sectional view of a circuit print board where a wiring hole 205 is provided to a resin board 203 and a radiation board 201 (a graphite sheet) is bonded to the circuit print board through an insulator layer 202. In FIG. 16, the resin board 203 and the radiation board 201 are contacted with a radiator 200. A wiring pin 204 is connected with a wiring pattern 206 through the wiring hole 205.
However, the prior art does not disclose a process for forming a structure shown in FIG. 16, so that how to form the structure is not clear. In other words, it is not clearly understood from the description of the above prior art when and how a step for bonding the radiation board 201 to the resin board 203 is placed in the manufacturing process of the circuit print board. It is not clearly understood from the description of the above prior art whether the radiation board 201 is formed by another process independent from the manufacturing process of the circuit print board, and so on. Especially, it is not clear how the insulator layer 202 provided to the side surface of the wiring hole 205 is formed so as to prevent the electrical connection between the radiation board 201 (the graphite sheet) and the wiring hole 205.
The present invention is provided to solve the above problems and aims to prevent the rise of the temperature of the heating element itself, the temperature of the circuit print board, the temperature of the frame of the electric device due to the heat radiated from the heating element such as the LSI and the power amplifier installed in the circuit print board as well as accomplishing down-sizing of the circuit print board.
Another object of the invention is to easily manufacture a circuit print board with a high efficiency of the radiation using manufacturing process of the circuit print board.
According to the present invention, a method for manufacturing a circuit print board includes:
a through hole making step for making a through hole penetrating a thermal diffusive sheet which is a carbon sheet bonded by substance supporting the carbon sheet; and
an insulator bonding step for forming a core by bonding insulator to a side surface of the through hole made at the through hole making step.
The above carbon sheet is a graphite sheet.
The method for manufacturing the circuit print board according to the present invention further includes:
a circuit patterning step for forming circuits on both sides of the core formed at the insulator bonding step;
a conductive hole making step for making a conductive hole penetrating the core with the circuits formed at the circuit patterning step; and
a connection step for placing conductive material to a side surface of the conductive hole formed at the conductive hole making step.
The method for manufacturing the circuit print board according to the present invention further includes:
a conductive hole making step for making a conductive hole penetrating the core formed at the insulator bonding step;
a circuit patterning step for forming circuits on both sides of the core having the conductive hole made at the conductive hole making step; and
a connection step for placing conductive material to a side surface of the conductive hole formed at the conductive hole making step.
Further, the method for manufacturing the circuit print board according to the present invention includes, before the through hole making step, a thermal diffusive sheet forming step for forming a thermal diffusive sheet by bonding substance supporting the carbon sheet to the carbon sheet.
The above insulator bonding step bonds the insulator to the side surface of the through hole by compressing the insulator to the thermal diffusive sheet having the through hole made at the through hole making step.
The above insulator bonding step bonds by plugging the insulator in the through hole made at the through hole making step.
The through hole making step makes the through hole having a greater diameter than the conductive hole made at the conductive hole making step.
According to the present invention, a method for manufacturing a circuit print board includes:
a patterning step for cutting a predetermined area from a carbon sheet; and
a core forming step for forming a core by bonding insulator to both sides of the carbon sheet from which the predetermined area is cut at the patterning step.
The above carbon sheet is a graphite sheet.
The method for manufacturing the circuit print board according to the present invention further includes:
a circuit patterning step for forming circuits on both sides of the core formed at the core forming step;
a conductive hole making step for making a conductive hole penetrating the core formed at the circuit patterning step; and
a connection step for bonding conductive material to a side surface of the conductive hole made at the conductive hole making step.
Further, the method for manufacturing the circuit print board according to the present invention includes:
a conductive hole making step for making a conductive hole penetrating the core formed at the core forming step;
a circuit patterning step for forming circuits on both sides of the core having the conductive hole made at the conductive hole making step; and
a connection step for placing conductive material to a side surface of the conductive hole made at the conductive hole making step.
According to the present invention, a circuit print board includes: multilayered circuits formed by laminating layers having interlayer insulator;
a carbon sheet provided between the multiple circuits and having a pattern made by cutting a predetermined area and
multiple conductive holes provided within the predetermined area-cut from the carbon sheet and plugged with conductive material for electrically connecting the multilayered circuits.
The above carbon sheet is a graphite sheet.
The above carbon sheet has the pattern made by cutting the predetermined area so as to be along a direction of thermal diffusion of heat radiated from a heating element mounted on the circuit print board.
The above carbon sheet has a pattern made by cutting an area from which heat radiated from a heating element mounted on a circuit print board is more difficult to be diffused rather than an area from which heat is easy to diffused.
A carbon sheet according to the present invention has a pattern made by cutting a predetermined area so as to be used for the circuit print board according to the present invention.